The invention relates to a radial piston pump having a pump body with two pump chambers lying on a straight line. Pump pistons displaceable along the straight line are disposed in the pump chambers, which pump pistons are moved upon a relative rotation of an actuator with respect to the pump body about an axis of rotation which bisects the straight line. At least one fluid duct is connected to each of the pump chambers at its end nearest the axis of rotation, which fluid duct is opened or closed depending on the positions of the actuator and pump body.
In a known radial piston pump of this general type (German Patent Application 36 15 885), which is to be used as a gas compressor, two pairs of pump chambers are present in a cross-shaped pump body, each pair of which lies on a straight line, the two straight lines intersecting each other perpendicularly at the axis of rotation. The rear ends of the pump pistons present in the pump chambers engage a guide which is formed by a housing rotating about the rotation axis, so that, upon rotation of the housing about the pump body, the pump pistons are displaced in the pump chambers along their respective straight lines, the pump pistons of one pair being moved simultaneously outwards or simultaneously inwards [i.e. the pump pistons lying on a common straight line move in the same sense of direction].
In the pump of German 3615885, fluid ducts are connected to the ends of the pump chambers nearest the rotation axis, which fluid ducts extend parallel to the rotation axis to one side of the pump body, while in the housing, on the same radius, openings are formed, which in certain rotation positions are located in alignment with the fluid ducts. These openings serve to allow gas to enter through the fluid ducts into the pump chambers and compressed gas to leave from them, while the compressing process is carried out when the fluid ducts are covered by the housing.
This known radial piston pump is suitable only as a compressor, because only one fluid duct is available for each pump chamber. Furthermore, sealing in the area of the fluid ducts is deficient because it is effected merely by the circular housing wall. Moreover the transition between closed fluid duct and completely open fluid duct takes place by means of a gradual modification of the opening cross-section of the fluid duct, which leads to a very uneven flow and conveyance pattern.
In another known radial piston pump (German Patent No. 24 36 627), several pump chambers are arranged radially in the pump body, and the actuator is mounted eccentrically relative to the center of the pump body, so that upon rotation of the pump body the pistons--coupled with the actuator--are displaced in the pump chambers. A pressure line and a suction line are located in the central region of the pump chambers and upon rotation of the actuator they are alternately connected with the pump chambers [the type of connection is not described in detail]. With this known radial piston pump, a specially designed coupling of the pump pistons with the actuator is necessary, because the pump body and actuator are not housed concentrically. This design is therefore relatively complicated.
Known radial piston pumps, such as described above, are suitable for many applications. If, however, small quantities of liquid (e.g. on the order of microliters) are to be conveyed uniformly and with a high degree of accuracy, not only are very precisely finished individual parts necessary, but control of the piston movement in precise co-ordination with the opening and closing of the fluid ducts of the pump chambers requires a considerable mechanical outlay. For this reason such piston pumps are used as single-part production units in the laboratory sector, but cannot be used in many applications because of high costs.
According to the invention a radial piston pump is designed in such a way that even very small quantities of liquid can be discharged very precisely in a controlled manner, the pump being of very simple design [e.g. so that it is even optionally disposable].
According to the invention, a radial piston pump is provided with pump pistons that are displaced in opposite directions by means of coupling with an actuator. Each pump chamber is connected to an intake fluid duct and to a discharge fluid duct, a valve arrangement being provided in each duct. The valve co-operates with operating means provided on the actuator, and the intake fluid ducts are connected to a common main intake duct and the discharge fluid ducts to a common main discharge duct.
With the radial piston pump according to the invention, the pump pistons lying on a straight line are moved in opposite direction so that fluid is drawn in into one pump chamber via its intake fluid duct, while fluid is discharged out of the other pump chamber via its discharge fluid duct, thus enabling fluid to be continuously conveyed at a pre-set rate. The fluid for both intake fluid ducts is drawn from a common main intake duct, and passed out of the two discharge fluid ducts into a common main discharge duct. The opening and closing of valve means for the intake fluid ducts and the discharge fluid ducts takes place in a precisely controlled way, because the actuator, which causes the forced or positive movement of the pump pistons by rotation about an axis of rotation and is provided with the operating means, moves the valve means for the fluid ducts into opened and closed positions. Thus, the movements of the pump pistons and the control of the valve arrangements for the fluid ducts are carried out synchronously in a precisely pre-set way, so that fluid is completely reproducibly conveyed in a pre-determined manner. This is especially advantageous if the radial piston pump according to the invention is used as an infusion pump in the field of medicine, because it can be used for the simple release of very small quantities of liquid per unit of time over relatively long periods at a constant feed rate, the intake volumes of the pump chambers possibly being of the order of microliters.
In a preferred embodiment of the invention, the actuator has at least one control disc rotatable about its axis of rotation, which control disc has at least one actuator surface for a pump piston and at which is provided an operating means for at least the valve means in the intake fluid duct of one pump chamber and in the discharge fluid duct of the other pump chamber. With this design a single control disc thus serves both to move one pump piston and to operate two valve arrangements, wherein it is also possible to provide the actuator surfaces for both pump pistons at this control disc and optionally to also provide the operating means for all valve means associated with it.
If a control disc with an actuator surface for one pump piston and an operating means for the valve means of an intake fluid duct and of a discharge fluid duct is arranged at one side of the pump body, a corresponding control disc with an actuator surface for the other pump piston and with an operating means for the other valve means can be mounted on the opposite side of the pump body and likewise on the axis of rotation, so that the actuator comprises two control discs, securely connected to each other, lying on both sides of the pump body, which control discs can be simply manufactured and fitted.
The operating means can each have an elastically deformable operating element secured non-rotatably on the pump body, operating projections being provided at the ends of said operating element on the side facing the pump body to act on the associated valve means, while the side of the operating element facing away from the pump body can be brought into engagement with cam faces formed on the control disc.
With such a design, a single operating element, secured non-rotatably on the pump body, serves to activate the valve means, for which cam faces provided on the control disc act on the operating element. In this way the elastic deformation of the operating element and thus the influencing of the valve means is effected by cam faces whose shape is exactly determined and unchangeable, thus achieving great accuracy.
To this end, cam followers can be provided on the side of the operating element facing away from the pump body, and, by engaging with a cam follower, the cam face can effect elastic deformation of an operating element to bring it into engagement with an operating projection.
A circularly arc-shaped extension of the cam face can be a recess for receiving the cam followers, ramps forming transitions to the cam face being provided at the ends of the recess, so that the area of the operating element carrying one cam follower is not deformed if the cam follower is located within the recess. The cam follower can slide over the corresponding ramp for the transfer from recess to cam face and back.
For the movement of the pump pistons by means of one or more control discs, each pump piston can be provided with at least one laterally projecting cam peg, which engages with the associated actuator surface of the control disc. In this way a defined mechanical allocation of control disc position to pump piston position is achieved, without the risk of the pump pistons tilting during displacement movements.
In order to provide a particularly simple design of the radial piston pump according to the invention which is suitable for feeding small quantities of liquid, each fluid duct can have a side opening and be surrounded in this area by a flexible sealing tube. To close the valve means, the operating element can push the part of the sealing tube located in the area of the opening through the side opening into sealing abutment against the wall of the fluid duct facing the opening, in order to close the fluid duct.
The wall facing the opening can be formed by an annular area which surrounds a section of the fluid duct running perpendicular to the central axis of the opening. In this way, the sealing tube can be pressed in a sealing manner against this annular area in order to securely close off the section of the fluid duct running perpendicular to the central axis of the opening.
The structure can be further simplified in that the openings of the two intake fluid ducts, and the openings of the two discharge fluid ducts, lie coaxially relative to each other. Sections running perpendicular to the central axis of the opening are joined to each other, the associated main duct being connected to these joints.
In this way the openings of both intake fluid ducts can be covered with a single sealing tube or sealing tube section and the openings of both discharge fluid ducts can be covered with another sealing tube or sealing tube section. By means of the associated operating elements one intake fluid duct and one discharge fluid duct can, for example, be alternately sealed off, while the other two fluid ducts are kept open, so that liquid is sucked in through the opened intake fluid duct from the main intake duct into an associated pump chamber, while liquid is forced out of the other pump chamber through the opened discharge fluid duct to the main discharge duct.